1. Technical Field
The present disclosure relates to a method for outputting freshness information, a freshness information output apparatus, and a non-transitory computer-readable recording medium used for outputting freshness information regarding a fish.
2. Description of the Related Art
In general, when the freshness of a fish is determined, an expert visually checks the appearance of the fish and the state of its surface and determines the freshness of the fish on the basis of color, luster, the state of scales, and the like. This method, however, depends heavily on the personal opinion of the expert. Therefore, a quantitative method, which can provide more objective evaluation, is desired.
As one of quantitative methods, a method in which an index K is measured is known. After a fish dies, related enzymes decompose adenosine triphosphate (ATP) in the fish's muscle in the following process.
Decomposition process: ATP→adenosine diphosphate (ADP)→adenosine monophosphate (AMP)→inosine monophosphate (IMP)→inosine (HxR)→hypoxanthine (Hx)
This decomposition process is the same in any kind of fish. As a fish deteriorates, ATP decreases and more inosinic acids and hypoxanthine are generated. The index K is defined as a ratio of the amount of inosinic acids and hypoxanthine to the total amount of the above-mentioned substances.
Because measurement of the amount of each substance for obtaining the index K involves chemical reactions, a lot of advance preparation is needed, and it takes time to complete the chemical reactions. In addition, part of the fish needs to be cut off before initiating the chemical reactions.
Since fish will be put on the table, a method for non-invasively evaluating the freshness of a fish, that is, a method that does not involve chemical reactions, is more desirable from a hygiene perspective.
As methods for evaluating freshness that do not involve chemical reactions, for example, a method for determining the freshness of a piece of meat by radiating polarized infrared rays onto tissues of the piece of meat and detecting the light intensity distribution of the polarization angle of transmitted or reflected light is disclosed as an example of the related art (Japanese Patent No. 4806285). In addition, a method in which near-infrared light having a stripe pattern in which bright portions and dark portions are alternately arranged is radiated onto a relatively transparent fish or shellfish and the freshness of the fish or the shellfish is determined using a contrast value of obtained image data having a stripe pattern is disclosed (Japanese Unexamined Patent Application Publication No. 2010-286262). Since these methods do not involve chemical reactions, freshness can be determined in a short period of time.